arm: omap: board-ldp: use generic dpi panel's gpio handling

The ldp board file currently requests gpios required to configure the NEC DPI
panel, and provides platform_enable/disable callbacks to configure them.

These tasks have been moved to the generic dpi panel driver itself and shouldn't
be done in the board files.

Remove the gpio requests and the platform callbacks from the board file.
Configure the gpio information in generic dpi panel's platform data so that it's
passed to the panel driver.

Signed-off-by: Archit Taneja <archit@ti.com>
Cc: Tony Lindgren <tony@atomide.com>